Photodynamic therapy (PDT) is a treatment that uses special drugs, sometimes called photosensitizing agents, along with light to kill cancer cells. The drugs only work after they have been activated or “turned on” by certain kinds of light. The light can come from a laser or other source, such as LEDs. PDT may also be called photoradiation therapy, phototherapy, or photochemotherapy.
The cancer cells absorb the light-sensitive drug. After being activated by light or laser, the drug releases a type of oxygen that kills the cancer cells.
Some healthy, normal cells in the body are also affected by PDT. These cells usually recover after treatment.
Photodynamic therapy (PDT) is a two-stage treatment that combines light energy with a drug (photosensitizer) designed to destroy cancerous and precancerous cells after light activation. Photosensitizers are activated by a specific wavelength of light energy, usually from a laser. The photosensitizer is nontoxic until it is activated by light. However, after light activation, the photosensitizer becomes toxic to the targeted tissue.
Several photosensitizer drugs are available today to treat a variety of diseases, including acne, psoriasis, age-related macular degeneration, and several cancers, such as skin, lung, brain, bladder, pancreas, bile duct, esophagus, and head and neck.
In addition to treating these conditions, PDT also helps treat bacterial, fungal, and viral infections. Studies have shown that this light-based therapy can trigger the body’s immune response, giving your body another means to help destroy cancerous and precancerous cells.
PHOTODYNAMIC THERAPY FOR CANCER
PDT can be used to treat some types of cancer. These include:-
- basal cell or squamous cell skin cancer
- head and neck cancers
- lung cancer
- a type of eye cancer called ocular melanoma
- other types of cancer, as part of a clinical trial.
A similar treatment called photodynamic diagnosis (PDD) can be used for:-
- some types of brain tumors
- bladder cancer.
PDD helps to diagnose and treat these cancers at the same time. The light-sensitive drug makes cancer visible so that a surgeon can remove it.
When PDT is used to treat early-stage cancers, the aim is to cure cancer. When PDT is used for more advanced cancers, the aim is to shrink cancer and reduce symptoms.
Researchers are trying to find out which types of cancer PDT works best for. Clinical trials are looking at new:-
- light-sensitive drugs
- laser light treatments
- non-laser light treatments
- ways of reducing the side effects.
Sometimes PDT cannot be used. This depends on where the cancer is in the body. Your hospital doctor can tell you whether PDT is the right treatment for you.
PHOTODYNAMIC THERAPY FOR PRECANCEROUS CONDITIONS
PDT is also used to treat some precancerous conditions, including:-
- Bowen’s disease – It is the growth of cancerous cells in the outer layer of the skin (epidermis). It is a very early form of slow-growing skin cancer. It often appears as a red, scaly area on the skin. Bowen’s disease is sometimes called squamous cell carcinoma in situ. This means the cancerous cells are in the outer layer of the skin. They grow very slowly and are unlikely to cause a problem in most people.
- Actinic keratoses (also called solar keratosis) – Scaly dry patches of skin caused by sun damage
- Vulvar intraepithelial neoplasia (VIN) – It describes abnormal changes of the cells that cover the vulva. The vulva is the name given to all the visible sex organs that surround the opening of the vagina outside the body. People who have a vulva can include women, trans men, and people assigned female at birth. VIN is not cancer, but it may develop into cancer after many years.
PDT DRUGS APPROVED IN US TO TREAT CANCERS
Several photosensitizing agents are currently approved by the US Food and Drug Administration (FDA) to treat certain cancers or pre-cancers. Here are two of the most widely used:
- Porfimer sodium (Photofrin) is a very widely used and studied photosensitizer. It’s activated by red light from a laser. It’s approved by the FDA to treat patients with certain kinds of cancers of the esophagus and lung and is being studied in other types of cancer.
- Aminolevulinic acid (ALA or Levulan) is a drug that’s put right on the skin. It’s used to treat actinic keratosis (AK), a skin condition that can become cancer, and is used only on the face or scalp. A special blue light, rather than laser light, is used to activate this drug.
Researchers are always looking for new PDT drugs, and new ways to give them. PDT is also being combined with other types of treatment, such as surgery and radiation therapy. Future possibilities include other combination treatments with PDT drugs, as well as new PDT drugs that can target tumor cells better, can leave normal cells more quickly, and allow the treatment light to penetrate deeper.
